1. Field of the Invention
The invention relates to a screw displacement pump of single-entry, double-shaft construction with an external bearing of two screw shafts and a pump housing enclosing the screw shafts by forming feed chambers and externally delimiting the feed chambers with its internal shell surface, as well as a suction chamber for the medium to be induced and a pressure chamber to accommodate the medium pumped by the screw shafts.
2. Discussion of Background Information
Many screw displacement pump concepts are known, e.g., a double-shaft, double-entry embodiment according to EP 0 699 276 B1, which is used, in particular, for pumping untreated crude oil/water/gas mixtures exiting from one very large well or from many, in part more than 500, small wells. Double-entry screw pumps have a housing subdivided into a suction chamber and a pressure chamber. The feed screws run either directly in the housing or in an exchangeable housing insert that is inserted into the housing between the suction chamber and the pressure chamber. The housing thereby serves, on the one hand, to provide a sufficient compressive strength to absorb the process pressure and, on the other hand, to provide the shape and positional stiffness to maintain the sealing-gap tolerances required for the pressure-increasing process among the feed screws and between the feed screws and the housing or the housing insert, with the feed screws, running in a non-contact manner, placing particularly high demands on the sealing gaps that are as small as possible, in order to achieve a high efficiency.
Screw displacement pumps embodied in a double-shaft, double-entry manner are technically very complex, cost-intensive in terms of production and servicing and are thus preferably used for larger pump performances that are typically already too large for pumping single wells (single-well boosting).
From DE 715860 B1, a mixed-flow pump for pumped liquids is known that has a single-sided external bearing for the feed screws. The feed screws are enclosed by a housing embodied as one piece and flange-connected to a housing part in which the screw-shaped rotors are supported. This housing can be removed for servicing tasks. If the pump has to be serviced, it is necessary to take the pump out of the feed line at the inlet and outlet pipes and to install a completely new pump.
Alternatively to a complete replacement, a screw displacement pump can be dismantled and repaired on site, which is very time-consuming. Furthermore, a pump assembly from several components at the customer's location has the disadvantage that a pump test with a precise determination of the performance data is impossible, so that as a rule a complete pump replacement is necessary to meet the required performance parameters.
Especially with single-well boosting there are high fluctuations in the composition of the medium to be pumped. States of pumping 100% liquid and phases of pumping 100% gas alternate in a largely unpredictable manner, whereby the phases of pumping 100% gas are particularly critical for screw displacement pumps, since with conventional screw displacement pumps the sealing, cooling and lubricating liquid is removed after a certain time of gas pumping. This causes a heating of the feed screw displacements and, associated therewith, a contact of the feed screws with one another and with the feed housing, which causes a higher wear, and possibly a stoppage of the pump. The problems thus arising in terms of servicing on site have already been described.
In addition to screw displacement pumps, eccentric screw pumps are also used for single-well boosting. The eccentric screw pumps are suitable only to a limited extent for pumping multi-phase mixtures, as their capability of pumping 100% gas is very limited in terms of time because of the friction heat being produced.
As a result of the oversizing of multi-phase pumps in a double-shaft, double-entry embodiment and for lack of suitable multi-phase pumps with lower output, thousands of oil wells all over the world are not or are no longer being worked. This means that valuable raw materials are not being used.